Means for preventing inductive disturbance in the test-circuits of telephone-switchboards.



' l H. M BASCOM.

MEANS FOR PREVENTING lNDUCTlVE DISTURBANCE IN THE TEST CIRCUITS 0FTELEPHONE SWITCHBOARDS, 1,1?5 111,

APPLICATION FILED JUNEZI, 1915- Patentd Mar. 14,1916.

lnv ehta r Henry M Base-om,

To all whom it may concern:

panama srn rns PATENT W E 7 HENRY IVE. BASCOM, F BROOKLYN, NEW YORK,ASSIGNOR T0 AMERICAI AND TELEGRAPH COMYANY, A CORPORATION OF NEW YORK.

MEANS FOR PREVENTING INDUCTIVE DISTURBANCE IN THE TEST-CIRCUITS OFTELEPHONE-SFNITCHBOARDS. L

Be it known that I, HENRY M. 'BASCOM, residing at Brooklyn, in thecounty of Kings and State of New York, have invented certainImprovements in Means for Preventing Inductive Disturbance in the Test-Circuits of Telephone Switchboards, of

which the following is a specification.

In telephone central station equipment it is convenient to carry inproximity to one another, as in a common cable between the operatorspositions and the relay rack, the test conductors which join-the tips ofthe trunk operators calling plugs with the'back contacts of the busytest relays and the conductors which'connect the mechanical locking keysof machine ringing systemswith the windings of the tripping relays. 'Byway of the capacities. between these two groups of conductorsalternating current flows from the ringing generator through the trunkoperators equipment to ground, producing noise in the receiver; To pre-.vent this is the object of'the present invention. I

In the accompanying drawing, Figure l W tend to be approximately equal,"and, on account of their relation, the efiect ofthc representsdiagrammatically a. telephone op- A erators equipment, and in muchsimplified -or schematic form those elements of the systhe repeatingcoil which I employ.

At an operators position A are situated calling plugs in which trunksterminate 'thesebeing here represented merely by tip contacts 10 of thegroup of plugs and test conductors 11 leading thereto. Mounted inthe-usual manner atthe position are machine ringing'keys, conventionallyindicated by contacts 12 to which are joined conductors 1.8. Eachoperator'has the customary telephone set, comprising :the receiver R andtransmitter T, the receiver being in circuit with the secondary winding14 of a repeat in-g induction coil or connecting device I.

, From-the plugs and keys the conductors 11 and 13 pass through a cableG to the relay rack B, where are mounted the busy test.

relays-o and the tripping relays' rfl' 'Ihe conductors 13. receivealternating current through the windings of the stripping relays from aringing generatonG. Thecon Specification of Letters Patent.

secondary winding 14..

test relays, in accordance with this --inven tlon, are connectedalternately in multiple 'rnnsr ndnn Patented Mar. 14L, 191%.

Application filed June-21,1315. Serial mi. 35,328.

by twoconductors 16 and 17 to primary WindihgslS and 19 respectively,.ofthe repeating coil I1. Thewindings or. this coilare: arranged upon thecore 20v and differ entially connected, as isparticularly-illustrated-in Fig.-. Qof'the drawing, s0 that curv I rentsflowing at the same time in the pri- 1 Y maries 18 and 19 produce equaland opposite effects uponthe core 20, and thus neutralize one another asregards thelr action upon the .lonsidering alternating current flowingfrom the generator in. one or more'of the conductors 13, it willtraverse the capacities between said conductors andthe conductors 11 inthe cable C,'back contacts 15 of relays r-which are notat this timeenerglzed as a result of the use of the trunks for connectlons,conductors 16 and '17 and primary primaries from the alternateconnections disturbing current upon the secondary winding isneutralized, and inductive disturbance in the -'operators receiver Rfrom this source is practically eliminated. Save-as above describedtheelements or" the system act in awell known manner and will thereforenot beconsidered further.

Having thus described my invention, 1 claim nation with a' plurality oftest conductors exposed toinductiveldisturbance, of an oper so 1. In atelephone switchboard, the combi- ,atorstelephone,.and a connectingdevice sit- .uated-between said plural conductors and the telephoneandincluding means whereby the inductive efiects are'neutralized.

2. Ina telephone switchboard,the-combi nation with a pluralityof testconductors exposed to inductivedisturbance, of an option between saidplural conductors and the telephone in which theinduced disturbingcurrents oppose one another.

3. In a telephone switchboard, the combination witha plurality of testconductor's erators telephone, and an inductiveconnecexposed toinductive disturbance, of a, re-

ary winding, and an operators telephone in circuit with the secondarywinding.

4. A switchboard cable containing a group of test conductors and aconductor carrying disturbing current, a repeating coil having twopr1mary windings to which the test conductors are alternately connectedin multiple and a secondary winding, the primary windings being arrangedto produce opposite inductive effects in the secondary winding, and atelephone connected to the secondary winding.

In testimony whereof, I have signed my name to this specification in thepresence of two subscribing witnesses, this'ninet'eenth day of June,1915.

HENRY Witnesses:

JOSEPH A. 'GATELY, JOHN B. HYNES.

M. BAs'coM; a

